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Interpretation of the P-T-XCO2 environment during metamorphism of carbonates, central Utö, Stockholm archipelago.
Stockholm University, Faculty of Science, Department of Geological Sciences.
2013 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

This thesis attempts to interpret the metamorphic condition and fluid composition experienced by metacarbonates on Utö, located in the south-eastern parts of the Stockholm archipelago. Utö is a part of the Svecofennian domain, and the area Bergslagen, that has hosted several mines over the last millennia. The bedrock in this area has been dated by the U-Pb technique to 1.90-1.87 Ga, placing it in the Paleoproterozoic era (Allen et al. 1996, Lundström et al. 1998). The rocks, of the studied area on the island of Utö, are mainly metacarbonates with a varying purity and thin layers of volcanic ash. These rocks become more felsic towards the north-western coast as the layers of felsic ash become more dominant.

To determine the P-T-XCO2 of metamorphism, metacarbonates were examined, in the field, in thin sections and mineral chemistry was determined by SEM analysis. Three samples were collected along a 1km transect, along which the assemblage calcite + dolomite + quartz + tremolite + diopside was observed. Petrographic and SEM analysis were performed to gather chemical data from coexisting calcite and dolomite in order to calculate temperature using the calcite-dolomite geothermometer. Chemical data from the SEM analysis were also run with AX and THERMOCALC together with pressure data received from a study by Engström (2011) of the adjacent island, Persholmen, to generate a T- XCO2 diagram. Pressure was estimated to 3.1 +/- 1.3 kbars, temperature calculated to 442°C 30°C and XCO2 to range from 0,00067-0,0038 with the standard deviation taken in to account. These results record equilibration with a CO2-bearing hydrous fluid at greenschist facies conditions.

Place, publisher, year, edition, pages
2013. , 23 p.
Keyword [en]
Metacarbonates, THERMOCALC, Utö, Calcite-Dolomite geothermometer, Fluid composition, SEM, Greenschist facies.
National Category
URN: urn:nbn:se:su:diva-93279OAI: diva2:645956
Metamorphic map of Sweden
Available from: 2013-10-02 Created: 2013-09-06 Last updated: 2013-10-07Bibliographically approved

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